1. Field of the Invention
The present invention relates to a fixing structure for detachably fixing an object to a base such as a rotational drum or the like.
2. Description of the Related Art
A photosensitive member, (referred to as a print plate hereinafter) which is formed such that a photosensitive layer is formed on a thin, sheet-shaped support which is made of aluminum, is used for printing. An image is recorded on the print plate in an exposure step and the exposed print plate is developed in a development step. Then, the resultant print plate is used as a machine plate for printing. A longitudinal dimension and a horizontal dimension of the print plate (machine plate) are different depending on sizes of printed matters.
As an image exposure device for a print plate, a device is known in which a print plate is wrapped around a rotational drum so as to be integrally held, the rotating drum is rotated at a high speed and a light beam in accordance with image data is irradiated onto the print plate, thus the print plate is scanned and exposed.
In this type of the image exposure device, as a structure for fixing a print plate to a rotating drum, a structure is known which clamps and fixes non-image portions of both ends of a print plate along the circumferential direction of the rotating drum with respect to an outer circumferential surface of the rotating drum. In the fixing structure, a clamp portion is urged to the rotating drum side by an urging force of an urging means, and the print plate is clamped and fixed between the clamp portion and the outer surface of the rotating drum.
However, in a case of this fixing structure, there is a structural drawback that when the rotating drum is rotated at a high speed, a centrifugal force acts on the clamp portion in a direction opposite a direction of clamping and fixing, thus a force of clamping and fixing is inevitably decreased. Further, there is a drawback that the print plate itself comes up off the drum due to an action of the centrifugal force so that deviation of print plates may be generated. These drawbacks cause image recording failures such as offset of positions of images, light beams being out of focus and torsion of images recorded on the print plate, and the like. As a result, the finish of printed matters may be poor.
Next, a description will be given of a chuck-type fixing structure which is similar to the above-described clamp-type fixing structure. The chuck-type fixing structure has a chuck. The chuck presses and fixes side edge portions of a print plate along the circumferential direction of a rotating drum to the outer surface of the rotating drum. A plurality of grooves, whose cross-sections are formed in an up-side-down T-shaped configuration and which extend in the circumferential direction of the rotating drum, are formed in parallel at the outer surface of the rotating drum so as to correspond to print plates of various sizes. It is structured such that a base portion of the chuck (so-called fixing piece) is mounted to one of the grooves and the chuck can be moved along (and fixed to) the groove.
FIG. 19 shows a relationship between the chuck of the above-described fixing structure and the groove. In FIG. 19, a groove 212 formed at a rotating drum 210 includes a narrow width portion at an entrance side and an enlarged width portion 214 whose cross-section is formed in a rectangular configuration at an inner side (center of drum side).
A chuck includes a thin and round bar-shaped supporting shaft 218, a base portion 216, i.e., a fixing piece 216 which is formed in a substantially rectangular shape such that longitudinal direction end portions are round. The longitudinal dimension of the fixing piece 216 is substantially the same as the width dimension of the enlarged width portion 214 of the groove 212, and a length of the fixing piece 216 perpendicular to the longitudinal direction thereof is shorter than the width dimension of the narrow width portion of the groove 212.
When the chuck is mounted and fixed to the drum, firstly, the fixing piece 216 of the chuck is inserted into the enlarged width portion 214 through the narrow width portion of the groove 212. Then, the supporting shaft 218 is rotated about 90xc2x0 about its axis. At this time, the fixing piece 216 is also rotated about 90xc2x0 within the groove 212 (the enlarged width portion 214 of the groove 212). Therefore, the fixing piece 216 cannot be removed from the enlarged width portion 214 of the groove 212. That is, the chuck (the fixing piece 216) is fixed to a rotating drum 210.
The following drawbacks arise in the above-described fixing structure. That is, when the rotating drum 210 is rotated at a high speed in order to carry out exposure, a centrifugal force acts on the chuck (the fixing piece 216), and a force to bend the peripheral edge of the opening portion of the groove 212 is applied thereto. As the thickness of the peripheral edge of the opening portion is thin, the peripheral edge of the opening portion deforms upwards and the fixing piece 216 is removed from the groove. Further, if the peripheral edge of the opening portion is deformed, there may be an undesirable case in which adhering of the print plate to the outer circumferential surface of the rotating drum may be poor.
In order to avoid damage of the peripheral edge of the opening portion of the groove, the peripheral edge of the opening portion needs to be made thicker, however, in order to make the peripheral edge of the opening portion thicker, the thickness of the rotating drum needs to be thick. As a result, the weight of the rotating drum is inevitably increased.
The present invention provides a fixing structure which can solve the above-described drawbacks. Further, the present invention provides a fixing structure which can detachably fix an object to a base such as a rotating drum or the like without using a complicated mechanism. The present invention provides a fixing structure which, when a sheet material such as a print plate or the like (fixing member) is wrapped around the base, the sheet material can be securely fixed to the base.
An aspect of the present invention is a chuck for detachably fixing an object to a rotatable base, the chuck comprising, (a) a support detachably mountable to the base, (b) a clamp having opposite ends, the clamp being pivotally mounted to the support between the ends of the clamp, and (c) a resilient member connected to one end of the clamp, the resilient member being resiliently deformed when the support is mounted to the base, which applies a force to the one end of the clamp, thereby causing the other end of the clamp to pivot downward, and apply a pressing force against an object disposed between the base and the the other end of the clamp, wherein when the base rotates, centrifugal force acts on the clamp and increases the pressing force against the object.
Another aspect of the present invention is a fixing structure for detachable mounting, comprising, a base having a dovetail groove-type groove including a bottom and a top, formed along the base and whose cross-section is a substantially trapezoidal such that the groove has a width less than a width of the groove top, and an object having an end with a block integrally provided at the end of the object and the block being insertable into the groove, wherein the object is rotatable with the block about an axis of the object, and the block is structured such that when the object is positioned at a first rotation angle position around the axis of the object, the block can be inserted into the groove and when the block is rotated from the first rotation angle position to a second rotation angle position, the block engages with the groove and thus further rotation of the block is prevented and the block cannot be removed from the groove at the second rotation angle position.